1. Field of the Invention
The present invention relates to a hydraulic circuit for an automated twin clutch transmission for motor vehicles, comprising a countershaft transmission with two parallel power transmission branches, and two main clutches, comprising:
a high pressure circuit having at least one actuator for the countershaft transmission and/or the main clutches,
a low pressure circuit for lubrication and/or cooling of elements of the twin clutch transmission, and
a first adjustment pump for providing a variable high pressure for the high pressure circuit.
Further, the present invention relates to a twin clutch transmission having such a hydraulic circuit.
2. Description of the Related Art
It is a recent tendency to use automated countershaft transmissions and spur gear transmissions in motor vehicles. In such transmissions, manipulating drives operate the shift clutches, particularly synchronizer units, and the starting and separating main clutch.
These automated manual transmissions suffer from an interruption of the traction force during a shifting process, cf. xe2x80x9cAutomatisierte Kraftfahrzeuggetriebexe2x80x9d, Hans-Joachim Fxc3x6rster, Springer Verlag, Germany.
In contrast thereto, the so-called twin clutch transmissions can perform power shifts.
Twin clutch transmissions comprise two main clutches at the input side which can be manipulated separately from each other, wherein one of the clutches is usually assigned to the even gears and the other clutch is usually assigned to the odd gears. A gear change of successive gears is made by operating the two input side main clutches in an interleaving manner. The load at the input side is continuously passed from one power transmission branch of the transmission to the other branch. Thus, power shifts can be performed without interruption of traction force.
A hydraulic circuit for controlling a twin clutch transmission is partially disclosed in the xe2x80x9cAutomobiltechnische Zeitung ATZ 89 (1987, 9), Porsche twin clutch transmission (in the following referred to as xe2x80x9cPDKxe2x80x9d).
In the PDK, the hydraulic energy generation is divided into two circuits. A pressure-controlled adjustment pump working according to the vane-cell principle supplies the hydraulic control circuit. In the low pressure circuit that is used for lubrication purposes, a constant pump is operated. The two clutches are controlled by proportional pressure reducer valves. The three synchronizer units are each actuated by two 3/2-port control valves, i.e. in total six control valves.
The pressure controlled vane-cell pump for the high pressure circuit is operated on demand. The constant pump for the low pressure circuit supplies the oil in dependence on the speed of the combustion engine.
Constant pumps are advantageous as hydraulic energy supply systems in mobile applications, due to high robustness, low weight, small size and low costs. The supply volume is derived from the requirements at extreme conditions. For all other operational conditions, the supplied amount of volume flow exceeds the necessary amount of volume flow, cf. lecture notes of the lecture xe2x80x9cFluidtechnik fxc3xcr mobile Anwendungenxe2x80x9d, RWTH Aachen, 1st edition, 1990, Prof. Dr.-Ing. W. Backxc3xa9, Prof. Dr.-Ing. J. Helling.
In the PDK, the supply volume is determined both in the low pressure circuit as well as in the high pressure circuit by the hydraulic operation condition at low engine speeds. With increasing differential speed, the discrepancy between the available supply flow of the pump and the necessary volume flow of the loads increases. Excessive hydraulic power has to be dissipated as a loss volume flow, using a suitable valve control. The losses are generated in a tertiary energy carrier (chemicalxe2x86x92mechanicalxe2x86x92hydraulic). An electronic control of the pressure level can reduce the influence of the hydraulic circuit. It is the object to reduce the loss producing counterpressure.
Pressure-controlled adjustment pumps allow to adapt the volume flow to the demand. The dependency from the engine speed exists only at maximum adjustment. Thus, those pumps are close to being an optimum solution from an energetic viewpoint, because the volume flow has the highest contribution to losses.
Within a project DKG 430 it was proposed by the assignee of the present invention, to provide an adjustment pump not only for the high pressure circuit but also for the low pressure circuit. Thereby, the energy consumption can be further optimized. However, this solution needs improvement with respect to costs and weight.
For the control or closed-loop control of the clutch function, the PDK uses proportional 3/3-port pressure reducer valves. These valves convert an impressed magnetic coil current into a hydrostatic pressure. The hydrostatic pressure acts onto the manipulating area of a hydraulic cylinder and impresses a manipulating force onto the clutch mechanics.
The hydraulic mechanical closed-loop control is made via a mechanical balance at the valve gate.
Proportional pressure reducer valves have, in general, the following disadvantages:
The magnetic hysteresis results in a width of backlash in the hydrostatic pressure.
The hydraulic mechanical control of the pressure reducer valve is subject to thermal influences. Stability and attenuation are changed with changes in temperature.
In dynamic processes where volume changes arise in the hydraulic drive (cylinder), the direct pressure feedback cuts off or on the volume flow before the target pressure is achieved. This has a negative influence on the movements that have to be made. The open-loop transfer function in which elasticity, compressibility, friction and inertia act, does not allow an exact assignment of magnetic current to the momentary hydrostatic pressure of dynamic processes.
In general, the hydraulic clutch control of the PDK has the following disadvantages:
The dynamics limit the momentary supply volume of the pump. The adjustment process of the pump requires reaction time. In this time, the pump adapts its feed volume to the induced demand of the drives. A constant pump supplies the momentary supply flow of the pump. In the constant pump, an increase of the supply amount leads to higher losses at higher rotational speeds.
The lack of electronic feedback of the pressure is disadvantageous for the control optimization; any diagnosis for monitoring the clutch function is made difficult.
In the PDK, there exists a safety hazard because of transmission blockages in case of malfunctions of the pressure reducer valves.
The dry main clutches used in the PDK are difficult to control.
On the other hand, wet clutches need an active cooling oil control in view of the effect of the impressed cooling oil amount on the drag torque of the clutch; the constructional expenditure is increased if this object is to be solved by a magnetic valve.
The operation of the synchronizer units in the PDK is performed on an electro-hydraulic basis. Each synchronizer unit is controlled by a drive, consisting of a double-acting cylinder and two 3/2-port control valves. The cylinder drive comprises two springs. In a fail safe position, the cylinder is in its central position. In this cylinder position, the synchronizer unit is in its neutral position.
In view of the fact that each synchronizer unit needs a double-acting cylinder and two 3/2-port control valves, the PDK has high costs, requires a high technical expenditure and a large amount of elements.
The actuating forces cannot be proportioned with the control valves which are on-off valves. Thus, shift noises occur, the load on the elements is high, the synchronizer force cannot be adjusted and the position cannot be closed-loop controlled (neutral, synchronous).
In view of the fact that the fixation is made by means of springs, the pressure has to maintain the engaged gear, the costs are high. Further, disengagement of a gear has to be made by spring forces.
Also, there are no means for externally locking inadmissible actuations of synchronizer units.
It is also known in the art to actuate the synchronizer units of automated transmissions with a gear selector drum, which drum is driven by an electrical motor (e.g. DE 196 12 690 C1). Electrical motor manipulating drives have some advantages over electro-hydraulic drives, and are particularly easy to be controlled.
However, electric motor drives are disadvantageous in view of the mass of electro-hydraulic drives, the current load on the electrical onboard power supply, the large space required, the comparably low adjustment speed, and the comparably low available adjustment torque. Further, one electrical motor is necessary for each degree of freedom to be realized.
The mass moments of inertia are determined by the electrical motor and an associated spur gear stage.
In the field of continuously variable transmissions, it is further known (DE 195 46 294 A1) to connect the discharge opening of a pressure chamber with the input of a jet pump, the suction line of which being connected with a fluid reservoir.
The pressure chamber can be fed by a pump and serves to generate a hydraulic pressure which produces a bias force between taper-disk sections and a transfer steel band.
The jet pump is used to provide a larger fluid volume for lubrication and/or cooling purposes.
At the suction jet side of the jet pump, a check valve is provided which opens in suction direction. Thus, it is ensured that the oil volume arriving at the input side at low temperatures is fed to the elements to be cooled or lubricated.
In a paper prepared at the RWTH Aachen by Guido Reinatz with the title xe2x80x9cEinsatz von Strahlapparaten in Getriebenxe2x80x9d, 1991, the use of jet pumps for oil supply in hydraulic equipment is known.
In general, the use of jet pumps in transmissions of motor vehicles has two major disadvantages:
1. Jet pumps are hydrodynamic pumps and are largely dependent on the counterpressure. The large temperature range of motor vehicles, with changes in viscosity of three orders of magnitude, set a technical limit for hydrodynamic pumps.
2. Jet pumps are constant pumps. They may be arranged and optimized for a certain hydraulic and thermal operational condition. The optimum efficiency to be achieved is 50%. In all other operational conditions, considerable decreases in efficiency have to expected.
The object of the present invention is to provide an improved hydraulic circuit for an automated twin clutch transmission for motor vehicles.
The above object is achieved according to a first aspect of the present invention by a hydraulic circuit, as mentioned at the outset, wherein the low pressure circuit comprises a plurality of second pumps which are connected in parallel to the first adjustment pump.
Thereby, the power consumption can be lowered in many operational conditions.
It is particularly preferred and a second aspect of the present invention, if at least one of the second pumps is a jet pump, the driving jet side of which being connected to the output of the first adjustment pump.
Thereby, the at least one jet pump can either fully or at least for some lubrication and cooling purposes, replace a mechanically driven low pressure pump which would otherwise be necessary.
The supply of the jet pumps by means of a pressure-controlled adjustment pump makes the jet pump superior over a constant pump.
In a particularly preferred embodiment, the driving jet side of at least one of the jet pumps is connected to the output of the first adjustment pump via an on-off valve.
It is particularly preferred, if the on-off valve is temperature-controlled.
In accordance with another preferred embodiment is the suction jet side of the jet pump connected to an oil sump or a fluid supply via the on-off valve.
The concept of feeding the jet pumps by a pressure-controlled adjustment pump as well as the concept of controllability of the jet pump is superior over a constant pump. The efficiency of jet pumps is comparably low, making reference to the mechanical power that would have to be produced (approximately smaller than 50%). However, the mechanical power demand is not dependent from the engine speed and can be reduced to a volume flow of approximately zero when switched off.
The adjustment pump lowers the power demand in the high pressure circuit. In between shift processes, it is only necessary to provide a balance for leakages in the system and the active clutch.
The combination of controllable jet pumps and a pressure-controlled adjustment pump has several advantages over known supply systems of the low pressure circuit of an automated twin clutch transmission:
1. It is not necessary to provide a hydraulic mechanical pump for the low pressure circuit.
2. The energy consumption is lowered in many operational conditions.
3. The weight and the costs are lowered, particularly if the jet pumps are made of plastic material.
4. The drive torque that is determined by the adjustment pump is reduced during cold starts.
5. The arrangement of the jet pumps within the transmission is flexible, for instance close to loads, so that the counterpressure is reduced.
6. The availability is high due to lack of moving parts.
7. The wear of jet pumps is particularly low.
8. The pressure level in the low pressure circuit is lowered to smaller volume flows by grouping into partial circuits, and the lines are shorter.
The adjustment speed of the adjustment pump is sufficient for the objects in the lubrication and cooling circuit. By means of the use of the on-off valve (particularly a stop valve), no losses occur. The driving current for the jet pumps can be taken directly from the adjustment pump so that unnecessary attenuation losses (e.g. due to a check valve) can be prevented.
For the high pressure circuit, it is particularly preferred if an energy storage (i.e. gas membrane storage) is provided which is preferably decoupled from the low pressure circuit by a stop valve.
Thereby, the availability of the stored pressure oil is ensured. The combination of the energy storage (or hydrostorage) with the first adjustment pump gives raise to the following advantages:
1. Losses in between shift processes are minimized.
2. The system pressure is constant.
3. There is no influence from the engine speed.
Further, the energy storage shortens the closing times of the clutch and improves the closed-loop controllability due to nearly constant pressure conditions on the side of the system pressure. It is further advantageous that the supply current of the pump does not have an influence on the closure times of the clutch and on the shift function.
In accordance with a particularly preferred embodiment is the temperature-controlled jet pump with its driving jet side connected via a restriction to an output of the first adjustment pump, in parallel to the on-off valve.
Thereby, a basic supply of the devices of the twin clutch transmission to be cooled or lubricated, is ensured even if the on-off valve is switched off.
Preferably, the cross section of the aperture of the restriction is temperature-controlled.
Thereby, the basic supply can be adjusted in dependence on the temperature.
In accordance with another preferred embodiment, at least two jet pumps are arranged in series. Thereby, it is possible to connect the output side of one jet pump with the suction jet side of a second jet pump. Such an arrangement has a number of advantages. On the output side of the first jet pump, the counterpressure is lower. Higher output volume flows can be realized if the second jet pump is connected in series to the first jet pump (xe2x80x9cpipeline principlexe2x80x9d).
In accordance with another preferred embodiment, one of the jet pumps is connected to a cooler with its output side, wherein the output of the cooler is connectable to the suction jet side of another jet pump.
Thereby, the further jet pump is supplied with cooled oil from the cooler.
Generally, it is preferable if at least one of the jet pumps is connected with its output to a cooler.
It will be understood that this jet pump is preferably connected to the output of the first adjustment pump via a temperature-controlled on-off valve. At high temperatures, this jet pump is additionally switched on, and the oil is cooled.
It is advantageous if the output mixture volume flow of at least one of the jet pumps lubricates and/or cools the wheel sets and/or the shift clutches of the countershaft transmission.
In accordance with another preferred embodiment, the output mixture volume flow of at least one further jet pump cools the main clutches (the clutches arranged between the engine and the countershaft transmission).
Preferably, the low pressure circuit comprises four pumps, two of the four pumps being associated to the two main clutches, one to the transmission and one to the oil cooler.
If the four pumps are each connected to the output of the first adjustment pump via on-off and stop valves, respectively, 16 different shift conditions are theoretically possible. Thus, the lubrication and/or cooling of the transmission and/or the main clutches can be established as required.
Preferably, the jet pumps are controlled on the suction jet side and the driving jet side. Controlling the driving jet allows to adjust to the hydraulic demand. Locking the suction terminal avoids negative effects due to counterpressure in the mixture tube. A loss of driving current via the suction terminal is controllable. Namely, a decrease in oil temperature leads to an extreme increase in viscosity and, conclusively, in the flow resistance in the mixture tube.
The manipulating elements or actuators for the switchable or controllable jet pumps can be mechanical, hydraulical-mechanical, thermal-mechanical, and electrical-mechanical systems. It is preferred if the main clutch cooling is controlled on a hydraulic-mechanical basis, and if the basic cooling and the cooler flow is controlled on the basis of a thermal-mechanical concept. It is further preferred if all on-off valves are identical. If the switch position is passive, the lines for the suction jet and the driving jet are locked (or blocked). In the active switch position of the valves, these lines are released.
The manipulating elements for the thermal-mechanical control can be implemented as expansion elements (as are available from Behr-Thomson), or bimetal elements.
The jet pumps for the clutch cooling are preferably hydraulically controlled. An active control of the pressure can be conducted for instance via a hydraulic side function (auxiliary function) of the clutch valves, or via a magnetic valve (on-off valve or pressure control valve).
In accordance with a further aspect of the invention, the high pressure circuit comprises for each of the two main clutches an actuator and a proportional directional control valve.
A proportional directional control valve allows to electronically correct a magnetical hystereses and friction in the manipulating cylinder. Further, the closed-loop control quality can be increased by improving stability and attenuation. The timing of the control can be tightened by an electronic monitoring. Further, malfunctions of the clutch behavior can be determined early (diagnosis function).
The closed-loop control of the mechanical condition of the clutches is preferably implemented by a digital pressure control of the piston pressure in a single acting manipulating cylinder being the actuator. The modulation of the hydrostatic pressure is controlled via the input volume flow and the output volume flow.
It is particularly preferred, if the proportional directional control valves each have an initial position in which the associated clutch is open and in which a control output for a side function is locked.
Rather than locking the control output (passive side function), it is also possible to open the control output in the initial position (rest position), so that the control output is active.
Since a proportional 3/3-port directional control valve would be fully sufficient for the control purposes of the clutch actuator, it is possible by enlarging the functions in the hydraulic portion of the clutch valves, to save further magnetic valves. The clutch valves take over their job.
It is known in the art (direct shift gear box of the Volkswagen Lupo 3L), that a clutch valve switches the pressure line to the transmission actuator in a side function. In this case, the pressure line is locked in the currentless condition. The leakage of the downstream gate valves is reduced and the pressure in the pressure line is lowered.
In the present case, it is not only such a side function that is realized. It is possible within the frame of the invention, in addition or alternatively, to select manipulating drives for the synchronizer units and the shift clutches, to activate a clutch cooling, and/or to control clutch restrictions.
The hydraulic control of the clutch cooling as well as the selection, the locking and the release of manipulating drives are objects which are functionally connected to the respective clutch of a twin clutch transmission.
In general, it would be possible to utilize the condition of the clutch for control purposes. In this case, for example the clutch pressure may serve to select and/or lock manipulating drives for the synchronizer units.
In view of the fact that a proportional directional control valve is provided for each of the two clutches of the twin clutch transmission, it is possible to combine the side functions of the two valves.
It is particularly preferred if the proportional directional control valves each have another initial position, in which the associated clutch is closed and in which the control output is locked (or opened).
Thereby, the proportional directional control valve is enhanced by two shift positions. The side function which is integrated into the hydraulic section is based in this case on a two edge control. Thus, it can be achieved that the side function is not dependent on which of the two clutches is active and which passive, and is always constant. In a twin clutch transmission, one clutch is generally active and the other one passive. In this condition, the clutch valves are switched in an opposite manner. The side function can be chosen identical when using a two edge control, independent on these clutch valve conditions. It is to be understood that a symmetrical characteristic is particularly preferred.
It will also be understood that such a coupling of primary and side functions in a proportional directional control valve for a clutch provides that the control dependencies are unambiguous.
It is preferred if the two initial positions (or the two further positions) are opposite end positions of the proportional directional control valves.
Thereby, a symmetrical characteristic can be achieved.
It is further preferred if the proportional directional control valves for driving the actuators for the two main clutches are 4/5-port directional control valves.
It is preferred if the side function is used to release an actuator for a shift clutch of the countershaft transmission.
It is further preferred if the release of the actuator is made by a combination of the control outputs of the side functions of the two proportional directional control valves.
As indicated above, it is particularly preferred if the side function is the cooling of the clutch that is assigned to the respective proportional directional control valve.
In accordance with another aspect of the present invention, a hydraulic safety circuit is provided in the high pressure circuit, which prevents that the two main clutches are closed simultaneously.
Thereby, it is already in the area of the hydraulic circuit, that safety is provided to prevent transmission blockages, and not only at the mechanical end.
It is particularly preferred if the safety circuit comprises a logical reducer valve, wherein the control output is the smaller control pressure of the control pressures of the two actuators of the two clutches.
Thereby, it is comparably easy to compare the smaller control pressure of the actuators with a predetermined threshold. As soon as the smaller control pressure exceeds the threshold, there exists the danger that both clutches of the twin clutch transmission are closed. In such a case, appropriate safety measures are to be initiated.
In accordance with another preferred embodiment, another hydraulic safety circuit is provided in the high pressure circuit for a pressure sensor.
Thereby, a hydraulic emergency function can be realized by modulating the clutch pressure, if a pressure sensor breaks down.
It is particularly preferred if the further safety circuit comprises at least one restriction in a parallel branch, which provides a characteristic of pressure versus manipulating value of a valve for pressure control, wherein the manipulating value can be compared with a corresponding value of the pressure sensor.
Thereby, a modulation of for instance the clutch pressure can be made similar to a shift force control by means of a restriction control. The constant restrictions may either be activated on demand by an emergency valve, or act permanently within the control range of the clutch. The control oil flow is increased during shift processes only.
It is particularly preferred, if the control oil flow through the restriction is used for cooling/lubrication.
The inventive object is also achieved by a twin clutch transmission having a hydraulic circuit as described above.
Further advantages and features will become apparent from the following description of preferred embodiments. It will be understood that the above-mentioned features and those to be discussed below are not only applicable in the given combinations, but may also be present in other combinations or taken alone without departing from the scope of the present invention.
Particularly, the features of the invention can be applied to hydraulic circuits of any transmissions, not only twin clutch transmissions. Further, it is not necessary to divide the hydraulic circuit into a high pressure circuit and a low pressure circuit.